The wireless communications network has grown exponentially over the years. A Long-Term Evolution (LTE) system offers high peak data rates, low latency, improved system capacity, and low operating cost resulting from simplified network architecture. LTE systems, also known as the 4G system, also provide seamless integration to older wireless network, such as GSM, CDMA and Universal Mobile Telecommunication System (UMTS). The 3rd generation partner project (3GPP) network normally includes a hybrid of 2G/3G/4G systems. With the optimization of the network design, many improvements have developed over the evolution of various standards.
The exponential growth of mobile subscribers requires substantial increase of network capacity. However, the capacity of a given network access technology network is limited by the laws of physics. The current cellular network deployed, such as 3G, LTE, LTE-A, suffers from limited licensed spectrum availability restraining the potential capacity increase. Small cell technologies, such as Wi-Fi WLAN is ideally positioned to extend the current cellular network capacity. Wi-Fi appeals to many operators as a cost-effective mean of offloading large amounts of mobile data traffic especially indoor where most of the traffic is generated. Operators are already taking advantage of devices supporting Wi-Fi as a tool to meet capacity demands by letting the user offload manually its traffic on standalone networks.
IP Multimedia Subsystem (IMS) is an architectural frame for delivering IP multimedia services. Historically, mobile phones have provided voice call services over a circuit-switched (CS) network, rather than strictly over an IP packet-switched (PS) network. Alternative methods or delivering voice or other multimedia services over IP have become available on smartphones (e.g. VoIP or Skype), but they have not become standardized across the industry. IMS is an architectural framework to provide such standardization.
IMS is a new way to dial PS call on LTE/Wi-Fi instead of fallback to 2G/3G legacy CS call. Operators plan to support Voice over IP (VoLTE) or Wi-Fi connection (WFC) features y stages. As a result, VoLTE/WFC features in PS domain are not able to support all services in CS domain now. For example, emergency call, supplementary service, SMS over IMS, etc., these services are not supported for some operators in PS domain now. Even for the same operator, the capability of VoLTE and WFC may be different in different region. Similarly, for data services, different radio access technologies (RATs) of 2G/3G/4G/WiFi may support different data services in different region.
When a user equipment (UE) accesses a service on one domain failed, the UE can retry the service on other domain. However, if there is an existing service and UN tries to access a second service on the same domain and encounters error, then the UE may not able to retry the failed service on the other domain because the first service still exists and needs to communicate with the network continuously. Otherwise, service interruption is introduced to the existing service. This is particularly important to UEs that are equipped with a single radio frequency (RF) transceiver module. In such case, the UN can only establish multiple services on the same domain. Even with multiple RF transceiver modules, the same problem may exist if the network does not provide multiple services via different RATS.
A solution is sought.